It is often necessary to warm physiological fluids prior to introducing them into a patient. For example, blood is refrigerated during storage and is preferably warmed before being introduced into a patient during a transfusion. Because it is frequently necessary to warm the physiological fluid rapidly, for example during an emergency medical procedure where a large quantity of fluid is required, heat exchangers have been designed to warm the fluid as it passes from the container the patient.
A heat exchanger for warming blood during a transfusion, is shown in U.S. Pat. No. 2,910,981 (Wilson, et al.). This heat exchanger includes a central tube surrounded by a jacket to form a space between the jacket and tube for circulation of a warming fluid. The fluid to be warmed and administered to a patient passes through the central tube. The central tube and the jacket are integrally formed, and three-port valves are screwed into threaded receptables at opposite ends of the heat exchanger to provide access to the central tube.
U.S. Pat. No. 3,643,733 (Hall) shows a heat exchanger wherein an outer tube partially covers an inner tube, the inner tube having fins which extend into the space between the inner and outer tubes for increasing heat transfer. Because of the different coefficients of expansion between the materials used in fabricating the inner and outer tubes, differential expansion occurs when the warming fluid begins to flow. To accommodate this differential expansion, Hall teaches an end bell held to an end of the outer tube by a spring and movable with respect to the inner tube.
The Hall heat exchanger is complicated in construction and permits a violation of sterility by movement of the end bell along the inner tube.